This invention relates to a cooling system for an outboard motor and more particularly to an improved arrangement for cooling the lubricating oil supply of an outboard motor.
It has been proposed to provide four cycle engines as the power source for outboard motors. Although four cycle engines have certain advantages over two cycle engines, they are basically more complex and this provides certain design challenges when applied to outboard motors because of the compact nature of such propulsion units. Specifically, if a four cycle engine is to be employed, it is the normal practice to provide a separate lubricant storage reservoir for the lubricant of the engine. An outboard motor presents a particular problem in this area because of the fact that the engine is normally mounted so that its crankshaft rotates about a vertically extending axis. This makes it difficult to employ a wet sump engine as is typical with most applications for four cycle engines.
Thus, dry sump systems are employed and this then presents a problem as to where the lubricant sump is located. If it is positioned beneath the engine in the power head then the engine becomes relatively high and the center of gravity of the outboard motor is elevated to an extent more than desirable. It is not practical to place the oil reservoir in the power head on the sides of the engine due to the desire of maintaining a compact construction, particularly of the power head so that it does not obscure rearward vision.
Therefore, it has been the practice to position the oil reservoir in the drive shaft housing of the outboard motor or at least partially therein. This, however, raises other problems.
In conjunction with most outboard motor practice, the exhaust gases from the engine are discharged downwardly through the drive shaft housing for discharge below the water so that the water in which the watercraft is operating can be employed at least partially for sound deadening. Frequently, it is also the practice to provide an expansion chamber in the drive shaft housing for assisting in silencing the exhaust gas noises. This, however, thus exposes the lubricant reservoir to the heat of the exhaust gases. Therefore, the lubricant for the engine may tend to become overheated due to the inherent operation of the outboard motor. For this reason it has been proposed to provide an arrangement wherein at least some of the cooling water from the engine is drained in proximity to or over the outer periphery of the oil pan so that it may be cooled. An example of a prior art type construction where this is done is shown in FIGS. 1 and 2 with FIG. 1 being a side elevational view of a conventional outboard motor of this type and FIG. 2 as an enlarged cross-sectional view showing how the coolant is delivered to the exterior surface of the oil tank.
An outboard motor constructed in accordance with a conventional practice employing a four cycle engine with a separate lubricant storage system is indicated generally by the reference numeral 11. The outboard motor 11 includes a power head that is comprised of a water cooled four cycle internal combustion engine, indicated generally by the reference numeral 12 and which may comprise any known type. The engine 12 is surrounded by a protective cowling which is comprised of a lower tray portion 13 and an upper, main cowling portion 14. The main cowling portion 14 is detachably connected in a known manner to the tray portion 13.
As is typical with outboard motor practice, the engine 12 is supported on a supporting plate 15 with its output shaft rotating about a vertically extending axis. This output shaft is coupled to a drive shaft 16 that depends into a drive shaft housing 17 having an outer housing portion 18. The lower end of the drive shaft 16 drives a propeller shaft 19 that is journaled within a lower unit 21 through a bevel gear transmission 22. A propeller 23 is affixed to the propeller shaft 19 in any known manner.
The outboard motor 17 is coupled to a combined clamping swivel bracket assembly, indicated generally by the reference numeral 24 for steering movement of the outboard motor 11 about a vertically extending axis, for tilt and trim movement about a horizontally extending tilt axis and for attachment in a known manner to the transom of an associated watercraft.
The engine 12 is provided with a lubricating system and lubricant is supplied for this system and drained back from it to a lubricant reservoir 25 that is mounted within the drive shaft housing 17 on the underside of the spacer plate 15.
Referring now specifically to FIG. 2, it should be noted that the oil pan 25 has an exterior wall 26 that defines an internal cavity 27 in which the lubricant is contained. The spacer plate 15 is formed with a cooling jacket 28 that is defined by an interior wall 29 and an exterior wall 31. Coolant is delivered from the engine cooling system to this cooling jacket 28. This is done in any known manner.
A gasket 32 is interposed between the drive shaft housing 18, oil pan 25, and the interior of the drive shaft housing 18. A plurality of small weep openings 33 are formed in the gasket 32 around the periphery of the oil pan 26 so that coolant will drain from the jacket 28 and impinge upon the outer walls of the oil pan 26 as shown by the arrows 34 in FIG. 2.
Although this construction has some advantages, there are also certain disadvantages. First, the cooling water is not very equally distributed along the outer periphery of the oil pan 26. In addition, either this cooling water or water which may splash up from the interior of the drive shaft housing 17 can impinge upon the walls 26 and leave deposits which may be corrosive. This is particularly true when operating in a marine environment inasmuch as salt deposits may be formed on the outer surface of the oil pan 25 and specifically its wall 26. Also, the distribution of cooling water around the outer periphery of the wall 26 cannot be ensured. Those weep openings 33 that are disposed closest to the discharge point of water from the engine cooling jacket will receive the most water and other areas will receive little water. Also, when the engine is running at low speeds there will not be a large amount of water flow and hence very little cooling will occur.
It is, therefore, a principle object of this invention to provide an improved oil pan and cooling arrangement for an outboard motor.
It is a further object of this invention to provide an oil pan arrangement for the engine of an outboard motor wherein a copious and uniform supply of water can be supplied over the outer periphery of the oil pan.